The abrupt change of ionic conduction with temperature is one of the most typical features of superionic crystals. Solid electrolytes are superionic crystals which are in a state of anomalously high ionic conduction. This state is connected with the disordering of ions from lattice to interstitial sites. It is possible to characterize the system's state by the tcmperaturc and TWO parameters, which depend on the crystal properties, but not on the temperature; the behaviour of the system in the whole variation plane of these parameters was investigated. The plane of parameters can be divided into 8 regions: in 4 of them, with a change in temperature, single phase transitions are realized which take the form of an abrupt change in the concentration of interstitial ions (in 2 regions the concentration decreases with a rise in temperature, and in 2 the concentration increases); in 2 regions there are no phase transitions; and finally, in 2 regions, with a change in temperature, 2 phase transitions occur, one of which increases the interstitial concentration of ions and the other decreases it Thus, the presence of a finite temperature range of super-ionic conduction is possible. The respective temperatures of transitions were calculated.